Frs treated by Proteinase K was inoculated again
into 9K medium without fluorine and with 40 mg/L
fluorine, respectively. The results are shown in Table 2,
in which “√” means that the cells can survive, in contrast,
“×” means not. Survivorship here was defined as the
ability to raise solution redox potential to about 600 mV
in 3 d. It shows that Frs could not survive normally in
solution containing fluorine. However, the ability of
growth in 9K medium without fluorine demonstrates that
the treated Frs was still active. These results indicate that
the tolerance of Frs to fluorine maybe was related to cell
wall or cell membrane proteins, and it is necessary to
clarify what proteins of cell wall or membrane are related
to the tolerance of the cells to fluorine in the next work.